1. Field of the Invention
The present invention relates to a long and thin flexible tube of an endoscope which is fitted with a built-in object, for example, a device for transmitting an observed image. The present invention also relates to a method of producing such a long and thin flexible tube.
With the recent development of the endoscopic technology, there has been an increasing need for considerably long insert parts in medical endoscopes which are used to observe the inside of the small intestine, and also for industrial endoscopes. Small-intestine, endoscopes need insert parts with an overall length of about 4 m to 7 m, and industrial endoscopes need much longer ones, i.e., even an insert part with an overall length of from 30 m to 50 m.
2. Description of the Prior Art
FIG. 9 shows a typical conventional endoscope which is in the process of being assembled. Reference numeral 51 denotes a distal end part that incorporates an objective optical system and other elements, 52 a built-in object such as an image guide fiber bundle, 53 a flexible tube, and 54 a control part.
As shown in FIG. 9, the conventional flexible tube 53 is formed in advance as a single flexible tube with a uniform or locally varied hardness, and the built-in object 52 is inserted into the flexible tube 53 to assemble the endoscope.
Such an assembling method involves no serious problem as long as the overall length of the flexible tube 53 is less than about 2 m. However, when the overall length of the flexible tube is increased by a large margin as in the case of small-intestine endoscopes and industrial endoscopes, which have recently needed to have considerably long insert parts, the frictional resistance that occurs when a built-in object is inserted into the long flexible tube increases so that it becomes difficult to insert the built-in object. There is therefore a danger that the built-in object or the flexible tube itself may break during the inserting operation.